Prior to the publication of the Meditations in 1641, Descartes asked his friend and correspondent Marin Mersenne to circulate the manuscript for comment and criticism among a number of philosophers, including his fellow mechanical philosophers, Hobbes and Gassendi. These comments and Descartes' subsequent responses, were published as a lengthy appendix to the Meditations, the “Objections and Replies.” Despite the fact that Gassendi and Descartes shared a strong anti-Aristotelian sentiment, a consuming interest in natural philosophy, and a dedication to the establishment of a new, mechanical philosophy of nature, their arguments in the “Objections and Replies,” later amplified in Gassendi's Disquisitio metaphysica (1644), were heated, to say the least. This controversy signaled a major rift between the two founding fathers of the mechanical philosophy. What was really at stake between them?

Their conflict can be understood as yet one more episode in the ongoing confrontation between the Judeo-Christian belief in divine omnipotence and the classical Greek preoccupation with the intelligibility of nature.